The proposed research is designed to determine the loci of linguistic context effects in speech perception. One group of experiments uses an identification function shift paradigm to distinguish between pre- and post-perceptual context effects on identification of speech in which reaction time and identification response measures are analyzed. These investigate a number of lexical variables (early vs. late phonemes in words, lexically represented phrases, word frequency, sublexical morpheme units ect) and sentence context variables (semantic context, syntactic constraints ect). A second group of experiments use a cross modal priming technique and reaction time measures in order to determine the activation of perceptually ambiguous words in semantically and syntactically biased contexts. The theoretical approach developed in the proposal is that one class of information, lexical and phonological knowledge, is used directly by perceptual processes in analyzing the acoustic input. In contrast, syntactic, semantic and pragmatic knowledge are used post-perceptually to resolve ambiguity (e.g. to select the contextually appropriate lexical item if more than one lexical item is activated.) The goals are to determine what constraints exist on the classes of information that are used directly by perceptual processes. While the proposed research will employ a normal college age subject population, it may be the case that contextual information plays a different role in speech processing for other populations. Findings from the proposed research may provide a baseline against which to assess the performance of disabled populations and the consequence of the aging process for speech processing.